EP1667798A1 - Assembly of an electrodynamic fractionating unit - Google Patents

Abstract

The fractionation plant has an electrical energy store coupled on the output side to 2 electrodes, respectively held at a reference potential and supplied with a pulsed HV under control of an output switch, the electrode ends held at a given relative within a reaction vessel containing a process fluid in which the process material is immersed, so that a reaction zone is provided between them. The electrical energy store, the electrodes and the electrode leads and the reaction vessel are fully enclosed by an electrically-conductive housing connected to earth, the wall thickness of the housing matched to the penetration depth corresponding to lowest component of the Fourier spectrum of the pulsed electromagnetic field.

Description

Construction of an electrodynamic fractionation system

The invention relates to the construction of an electrodynamic fractionation system (FRANKA = fractionation system Karlsruhe) for fragmenting, grinding or suspending a brittle, mineral process material.

All systems that have become known so far and that were developed by means of powerful high-voltage discharges, in particular the electrodynamic process, for fragmentation, removal, drilling or for similar purposes for the processing of mineral materials, consist of the following two main components:

The energy store, i.e. the unit for generating an HV pulse, often or mostly the Marx generator known from high-voltage pulse technology, and the application-specific reaction / process vessel filled with a process liquid, into which the bare end area of a high-voltage electrode connected to the energy store is completely immersed. Opposite it is the electrode at reference potential, usually the bottom of the reaction vessel, which functions as a ground electrode, in a suitable embodiment. If the amplitude of the high-voltage pulse at the high-voltage electrode reaches a sufficiently high value, an electrical flashover takes place from the high-voltage to the earth electrode. Depending on the geometric conditions and the shape, in particular the rise time of the high-voltage pulse, the flashover occurs due to the material to be fragmented, which is positioned between the electrodes, and is therefore highly effective. Flashes only through the process liquid create shock waves in it, which are not very effective.

During the high-voltage pulse, the electrical circuit consists of the energy store C of the high-voltage electrode connected to it, the space between the high-voltage electrode and the bottom of the reaction vessel and the return line from the bottom of the vessel to the energy store. This circuit includes the capacitive, ohmic and inductive components C, R and L, which influence the shape of the high-voltage pulse (see FIG. 6), that is to say both the rate of increase and the further temporal course of the discharge current and thus the pulse power coupled into the load and, consequently, the efficiency of the discharge with regard to the material fragmentation. In the ohmic resistance R of this temporarily existing circuit, the amount of electrical energy Ri ^{2 is converted} into heat during the time of the discharge current pulse. This amount of energy is therefore no longer available for the actual fractionation.

This circuit represents a conductor loop through which very large currents, approximately 2 - 5 kA, flow through over a very short period of time. Such a structure generates intensive electromagnetic radiation, ie it represents a radio transmitter with high radiation power, and must be shielded with technical effort to avoid interference in the technical environment. In general, such a system must be shielded by protective devices in such a way that it is not possible to touch the live components during operation. This quickly leads to an extensive protective structure beyond the actual useful structure.

All systems known to date in which the electrodynamic method is used have an open structure, i.e. the assemblies of such a system are connected to one another by electrical lines (see FIG. 6).

When fragmenting stony material, as described for example in WO 96/26 010, connecting lines between the electrical energy store and the spark gap can be seen, which form loops through which current flows during the HV pulse. Plants for removing material (DE 197 36 027 C2), for drilling in rocky rock (US 6, 164, 388) or for inerting (DE 199 02 010 C2) each show simple electrical lines to the high-voltage electrode. The invention is based on the object of constructing a FRANKA system in its circuit during the high-voltage pulse in such a way that both the inductance and the ohmic resistance of the discharge circuit are kept to a minimum and at the same time the technical outlay for shielding against electromagnetic radiation and for Ensuring touch security remains limited to a minimum of effort.

The object is achieved by designing the fractionation system in accordance with the characterizing features of claim 1.

The energy storage device and its output switch, the latter usually usually a spark gap operated or triggered in self-breakthrough, the electrodes together with the supply line and the reaction vessel are completely in a volume with an electrically conductive wall, the encapsulation, while maintaining the electrical insulation distance from areas with different electrical potentials. The volume between the encapsulation and the assemblies built into it is kept to a minimum, thus reducing the inductance of the system to the inevitable minimum. This attention to electrical physics enables the shortest possible rise time for the discharge pulse, which is typical for the system.

On the one hand, the wall thickness is at least equal to the penetration depth of the lowest component of the Fourier spectrum of the pulsed electromagnetic field, and is therefore largely determined by it. On the other hand, the mechanical strength requires a minimum wall thickness. The necessary larger wall thickness from one or the other of the two conditions is taken into account during construction.

In this complete encapsulation, the electrode is connected to the ground side of the energy store at the reference potential via the capsule wall. The rest of the electricity through the energy The energy storage and the components that are temporarily at high voltage potential are central to the encapsulation.

This encapsulated structure allows an electrophysical and operationally advantageous structure, the features of which are further specified in subclaims 2 to 9.

Depending on the operating mode, the capsule wall has a removable area for stacking (baking) operation or an access for continuous introduction (claim 3). The capsule should be opened in sections anyway for repair work.

According to claim 3, for the continuous processing of fragments on the capsule wall at least one outwardly directed tubular connector made of conductive material for the loading and at least one other for the removal are attached. Because of the electrical shielding to the outside, these are dimensioned in the long and clear width in such a way that at least the powerful high-frequency components in the spectrum of the electromagnetic field generated by the high-voltage pulse do not escape through these nozzles or in these nozzles up to the opening m the environment at least to that to be weakened by law.

The energy store and the reaction vessel are spatially separated from one another in the encapsulation. According to claim 4 sits in one inner end wall region of the energy store and in the other end wall region the reaction vessel or is formed therefrom.

The encapsulation is a closed tubular structure and has a polygonal or round cross section according to claim 5. The encapsulation can be both stretched or angled at least once. The shape is structurally determined by the installation project. The simplest form is the straight one. Consequently, the electrode located at reference potential is centered in the end wall of the reaction vessel and the high-voltage electrode is centered at a distance from one another (claim 6). The high voltage electrode is connected directly to the output switch of the energy store. In the case of a Marx generator as an energy store, this output switch is the output spark gap. In this way, the form of the encapsulation results in the electrically inexpensive and insulation technology-appropriate coaxial structure, with which the requirement of the encapsulation and thus the smallest inductance typical of the system is met.

In the installation of the system one is not limited according to claim 7. The electrical energy store including the output switch is located in relation to the reaction vessel in the encapsulation spatially above or at the same height or spatially below.

Depending on the type of material to be fragmented, the electrode is at reference potential, usually ground electrode, central part of the front or sieve bottom or ring or rod electrode.

According to claim 9, the energy store is separated from the reaction vessel by a protective wall, so that the reaction space is separated from the area of the energy store in a liquid-tight manner.

The high-voltage pulse between the high-voltage electrode and the bottom of the reaction vessel, or the current from one electrode to the other, converts the electrical energy introduced into different energy components of a different type, including simply also in mechanical energy, ultimately mechanical waves / shock waves. The high-voltage electrode is encased in an electrically insulated manner in its jacket area up to the end area, with this end area protruding completely into the process fluid.

The completely shielded structure of the energy storage or pulse generator and process reactor in a common electrical rically conductive housing has several advantages over the conventional, open way of construction:

the inductance of the discharge circuit is or can be reduced to the inevitable minimum;

the ohmic losses in the high-voltage pulse circuit are also kept to an unavoidable minimum;

minimal inductance and minimal ohmic resistance of the pulse circuit lead to a more efficient discharge in the load, i.e. to a greater energy input into this. The somewhat closed structure of the system has decisive advantages with regard to electromagnetic radiation and protection against contact. During the entire time of the HV pulse, the discharge current flows exclusively inside the system. This is evident in any case for the outgoing current flowing from the energy store, comprising the pulse generator, via the high-voltage electrode and the load, reaction fluid with fractionation material, to the bottom of the reaction vessel, owing to the shielding function of the electrically conductive encapsulation.

The reverse current from the bottom of the reaction vessel to the energy store flows on the inner wall of the hollow cylindrical encapsulation, since the magnetic field built up by the discharge current flowing briefly in the system has the property of minimizing the area enclosed by the conductor loop. Due to the skin effect, this briefly flowing backflow flowing on the inside of the system wall only penetrates to a small depth, the frequency-dependent penetration depth, into the wall material. The penetration depth is known to depend on the electrical conductivity of the wall material and on the frequency spectrum occurring in the discharge current. With the usual rise times of the high-voltage pulses of approx. 500 ns, a characteristic natural oscillation period of the discharge circuit of approx. 0.5 μs and when using simple steels such as structural steel for the system wall, the depth of penetration into the inner wall is less than 1 mm. The wall thickness of the encapsulation on the one hand necessarily takes into account the lowest frequency of the Fourier spectrum from the electrical discharge due to the depth of penetration (skin effect) and the necessary mechanical strength due to the shape retention of the system. The higher minimum requirement of the wall thickness dominates for one of the two reasons. This means that no electrical voltages can occur on the outer surface of the encapsulation, which eliminates the need for contact protection, or its structure can be kept to a minimum. Electromagnetic radiation to the outside cannot occur either.

The coaxial system is compact, manageable and accessible for measurement and control purposes. The electrical charger for the energy storage does not have to be shielded. Its feed line can be routed through the bushing to the energy store in the upper interior of the housing without problems, possibly through a coaxial cable whose outer conductor contacts the housing.

The complete, metallic encapsulated fragmentation system is explained in more detail below with reference to the drawing. 1 shows the coaxially constructed FRANKA system, FIG. 2 sketch of the FRANKA system with partition, FIG. 3 sketch of the FRANKA system for continuous operation, FIG. 4 sketch of the FRANKA system with U-shaped encapsulation, Figure 5 Sketch of the FRANKA system with reaction vessel at the top, Figure 6 shows the conventional FRANKA system.

In Figure 1, the coaxially constructed FRANKA system is shown schematically in axial section. The continuous or discontinuous mode of operation is not respected here, here the electrical structure is in the foreground. The electrical charger for charging the electrical energy store 3 is also not indicated. From an electrical point of view, the coaxial structure is the most advantageous. A deviation from this would only be made due to design constraints. The high-voltage pulse generator consists of the electrical memory C, schematized as a capacitor, and the inductance L and the ohmic resistor R in series.

The high-voltage electrode 5 follows. From its electrical connection to the resistor R, it is electrically isolated from the end region to the surroundings by a dielectric jacket. It bends with its bare end region 4 in the process / reaction volume indicated by a lightning symbol and has a predetermined, adjustable distance from the bottom of the process / reaction vessel 3, which forms the lower part of the coaxial, hollow cylindrical housing 6.

The current flow during the high-voltage discharge takes place in the components along the axis of the hollow cylindrical housing 6, flows in at least one discharge channel in the process volume to the bottom of the reaction vessel 3 and then via the housing wall 6 back into the energy store / capacitor 1. The housing 6 is at the reference potential "Earth" connected.

The inductance L and the resistance R represent the system inductance and the system resistance, C indicates the electrical capacitance and thus the available storage energy via the charging voltage,

1/2 C (nU) ² , which should be implemented as much as possible in the process volume. In the case of a Marx generator as an HV pulse generator, its at least two-stage (n = 2), the individual capacitance C and the step charging voltage U as well as the number of steps n are decisive for the storage energy.

FIG. 6 shows a FRANKA system schematically in a conventional design, as it is and is simply constructed for many laboratory work. Coaxial variants of a FRANKA system are outlined in FIGS. 2 to 5:

FIG. 2 shows how the energy store 1 is separated from the reactor area 3 by a partition in the area of the high-voltage electrode 5. This should be installed in particular if there is splashing liquid due to the discharge process.

Figure 3 shows two openings in the encapsulation 6, one in the jacket area for filling in the reaction vessel 3, the second from the reaction vessel 3, for example through the bottom. This constructional measure enables continuous operation with loading and unloading.

FIG. 4 shows the U-shaped encapsulation 3. This type of construction could be preferred in the case of large systems due to the weights and manageability.

FIG. 5 outlines a design turned upside down, the reaction vessel 3 sits above the energy store 1. Such a design could offer itself in the case of gaseous or very light, whirled up process substances.

FIG. 6 shows the structure of conventional FRANKA systems, which as a fully functioning system are additionally encapsulated by a wall for shielding and as protection against contact. The large electrical loop is not minimized. In the case of a pulse, it acts as a strong transmitting antenna. For this reason, shielding is regulated by law in industrial use. LIST OF REFERENCE NUMBERS

1. Energy storage device 2. Output switch / spark gap 3. Reaction vessel 4. Forehead of the high-voltage electrode 5. High-voltage electrode with insulator 6. Encapsulation 7. Connection process vessel - encapsulation 8. Connection charger - encapsulation 9. Filler neck 10. Discharge neck

Claims

Claims: 1.Construction of an electrodynamic fractionation system for fragmenting, grinding or suspending a brittle process material, consisting of: a rechargeable electrical energy store (1), to the output of which two electrodes are connected, one of which is at a reference potential and the other via an output switch (2 ) on the energy storage device can be pulsed with high voltage in a reaction vessel (3), which is filled with a process liquid, in which the process material is immersed and in which the two bare electrode ends face each other with an adjustable distance, the reaction zone, the electrode which can be charged with high voltage (4) is surrounded by an insulating jacket (5) up to the free end area and this insulating jacket is also immersed in the process liquid in the end area, characterized in that: the energy store together with its output switch, the electrodes including the supply line and the reaction sgefaß completely in a volume with an electrically conductive wall, the encapsulation (6), and this volume enclosed by the encapsulation minidie wall thickness of the encapsulation is at least equal to the penetration depth corresponding to the lowest component of the Fourier spectrum of the pulsed electromagnetic field and at least that for has the necessary mechanical strength, the electrode is connected at reference potential (4) via the capsule wall to the ground side (8) of the energy store, the electrode which is subjected to high voltage is connected in the shortest possible way to the output switch on the energy store. 2. Structure according to claim 1, characterized in that for the batchwise processing of fragmented material, the capsule wall partially as removable or at least one access in the capsule wall. 3. Structure according to 1, characterized in that for the continuous processing of fragmented material on the capsule wall at least one outwardly directed tubular connector (9) made of conductive material for the loading and at least one further (10) for the removal, which in the Long and clear width are dimensioned in such a way that at least the powerful, high-frequency components in the spectrum of the electromagnetic field generated by the high-voltage pulse do not escape through these nozzles or are weakened in these nozzles at least to the extent prescribed by law until they open into the environment. 4. Structure according to claims 2 and 3, characterized in that the capsule wall is a hollow body, in one inner end wall area of which the energy store is located and the other end wall area of which forms the reaction vessel. 5. Structure according to 4, characterized in that the encapsulation has a polygonal or round cross-section and has an elongated shape or angled shape at least once. 6. Structure according to 5, characterized in that the electrode lying at reference potential is centered m the end wall of the reaction vessel, the high-voltage electrode is centered opposite and the latter is encapsulated in a coaxial way with the output switch of the energy store. 7. Structure according to claim 6, characterized in that the electrical energy store together with the output switch with respect to the reaction vessel in the encapsulation sits spatially above or at the same height or spatially below. 8. Structure according to claim 7, characterized in that the electrode is formed at reference potential as a central part of the forehead or as a sieve plate or as a ring or rod electrode. 9. Structure according to one of claims 1 to 8, characterized in that the energy store is separated from the reaction vessel by a protective wall.